The present invention relates to a rotary trowel for molding ceramics suitable for use in the molding of various ceramic products such as dish, bowl and the like by means of a jigger.
Heretofore, the method of rotary trowel type molding which comprises feeding a raw clay composition into gap between a rotatable gypsum mold attached to the shaft of a jigger and a rotary trowel provided above the gypsum mold so as to rotate, and calendering the raw clay composition to form a ceramic product on the surface of the trowel has been adopted largely.
Since the rotary trowel used in the above method comes into contact with the raw clay composition while rotating at a high speed (usually, about 300 rpm or above), the trowel surface is required to have an abrasion resistance and a smoothness enough to lessen the abrasion loss and improve the quality of product. Especially in the recent years, it is intensely desired to pattern the outer surface of ceramics finely, in proportion to which the trowel surface is readily lost by abrasion and lifetime of the rotary trowel is shortened. As a result, abrasion-resistance and smoothness of trowel surface have very important meanings. Further, in cases where the trowel surface must be patterned, the material constituting the trowel surface is required to have a high easiness of molding enough to form the concave-convex pattern easily and a high security of molding enough to form the fine pattern more exactly.
In the prior rotary trowel, a pattern is formed on the trowel surface by a mechanical fabrication (cutting or the like), or by mechanically fabricating a matrix followed by flame spray-coating a molten abrasion-resistant material onto the patterned matrix surface to form a film thereof.
However, mechanical fabrication is sometimes unable to form a fine pattern (that is, fine convexities cannot sometimes be formed by cutting fabrication though concavities can relatively easily be formed thereby), and requires a quite complicated procedure. Further, when the step of flame spraying coating is added thereto, the number of steps increases and a film of uniform thickness becomes difficult to form on the matrix surface, so that no fine pattern can be formed exactly.
Thus, it is the first problem of the present invention to provide a rotary trowel for use in the molding of ceramics which can retain a high abrasion-resistance and a high smoothness of trowel surface and, even when complicated patterns are given to the trowel surface, can form such patterns easily and exactly.
Further, as a modification of the rotary trowel type calender molding method, there can be referred to the hot trowel method which comprises generating a steam film in gap between the rotary trowel and the raw clay composition by heating the rotary trowel and thereby preventing adhesion of the raw clay composition to the rotary trowel and at the same time retaining a smooth contact between the rotary trowel and the raw clay composition. The rotary trowel used in the hot trowel method is usually heated to a temperature of 80-120xc2x0 C. by means of a heater or the like, and therefore the material constituting the rotary trowel is required to have a high heat resistance and a high heat conductivity enough to transmit heat to the trowel surface.
Thus, it is the second problem of the present invention to provide a rotary trowel for use in the molding of ceramics which retains a high abrasion-resistance and a high smoothness of trowel surface and, even in cases where complicated patterns are to be formed on the trowel surface, can form such patterns easily and exactly, and is excellent in heat resistance and heat conductivity.